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Horizons Regional Council has resorted to using a helicopter to carry out water quality monitoring at Lake Horowhenua, with health and safety concerns cited as the reason it won't send staff to the lake edge.

The chopper was spotted and filmed by locals hovering very low over the water last week, and Horizons has confirmed it was undertaking monthly water quality sampling at the lake.

The regional council's Freshwater and Partnerships manager Logan Brown said it was the first time the method had been used for Lake Horowhenua and it was being used as an alternative because council staff are unable to operate from the lake's edge due to health and safety concerns.

He would not elaborate as to what those concerns were and replied "no comment" to a question about whether they referred to any threats made against council staff if they were to visit the lake.

"Helicopter sampling is not the preferred method of sampling for Lake Horowhenua as we can't test for everything we need to by air," he said.

"Our preference is to do so by boat so we can service the water quality buoy as well as collecting water quality samples," he said.

"However, given the vital nature of this monitoring information in informing the restoration programmes that are currently occurring within the Lake Horowhenua catchment and the lake itself it was vital to continue collecting this information."

Mr Brown said the data collected allowed Horizons to "work out the health of Lake Horowhenua" and look at trends in water quality over time as they implement restoration programmes.

"We therefore needed to change monitoring methods to ensure that we can inform the public of the success of these programmes."

Horizons had been given permission to collect samples via helicopter by the Lake Horowhenua Trust and Lake Domain Board as it was preferable to avoid missing data points which would interfere with detecting water quality trends, Mr Brown said.

He was unable to say how much it had cost to use the helicopter as an alternative method, saying that as it was the first time they had used it at the lake so they could not be exact until the invoices came in.